Dr. Qingyu Yan, a Postdoctoral Research Associate at Rensselaer
Polytechnic Institute, gave audiences of Physics Department of UTA a
seminal talk. The talk is titled "Magnetic Functional Oxide by Plasma
Spray-MnZn Ferrites", Dr. Yan presented a systematic studies of process,
structure and magnetic properties of plasma-sprayed MnZn ferrites. These
materials are considered as the core material of miniaturized planar
inductors for high frequency applications. Materials with high
resistivity, stabilized permeability and low coercivity are desired for
the applications of high frequency inductor cores. With the advantages
of single step, low substrate temperature processing, bulk production
capability and cost efficiency, plasma spraying of ferrites offer a
promising route for applications in industry. The electrical and
magnetic properties of plasma-sprayed MnZn ferrites have been studied by
means of impedance spectroscopy, ferromagnetic resonance, vibrating
samples magnetometer, superconducting quantum interference devices
magnetometer and neutron diffreaction. The issues related to the plasma
spraying process of MnZn ferrites including cation disorder,
microstructural defects, inhomogeneous composition, and exciting of
meta-stable phases have been discussed in detail. These factors degrade
the functional properties of plasma-sprayed MnZn ferrities by decreasing
electrical resistivity, lowering the saturation magnetization and
increasing the coercivity. It is found that significant improvements of
both electrical and magnetic properties can be made through annealing
these MnZn ferrite films in air. The formation of insulating phase upon
annealing increases the resistivity; the ordering of thc cation
distribution increases coercivity. As a result, the permeability of the
plasma-sprayed MnZn ferrites can be stabilized to frequency range above
10 MHz, which upgrades the performance of the inductors to a level that
is comparable to that of ferrite inductors made by conventional
singering methods. Thus, plasma spraying of MnZn ferrites may offer a
promising route of fabricating miniaturized inductors or even other
related ferrites electronics for industrial applications. The analyses
developed in this study are not necessarily restricted to the study of
plasma-sprayed ferrite. The underlying principles, which govern the
functional property changes of ferrites after a high temperature and
rapid quenching process, may aid in generalizing ideas for improvements
of engineering processing of other functional oxides.